1. Field of the Invention
The present invention relates in general to compensation for the temperature of an automatic gain control circuit used in outdoor satellite communication transmitters, and more particularly to a technique for minimizing variations in an output intermediate frequency signal from the automatic gain control circuit based on external temperature variations.
2. Description of the Prior Art
Various methods have conventionally been proposed to compensate for the temperature of an automatic gain control circuit for satellite communication transmitters used in outdoor equipment. One such conventional temperature compensation method is to offset variations in an output signal from an intermediate frequency signal detector and in an output signal from a reference signal detector based on external temperature variations with respect to each other using a differential integrator. The intermediate frequency signal detector is adapted to detect an output intermediate frequency signal from the automatic gain control circuit and the reference signal detector is adapted to detect a reference signal. Another conventional temperature compensation method is to maintain the internal temperature of the outdoor equipment at a normal temperature using a heater. However, the first conventional temperature compensation method has a disadvantage in that the output intermediate frequency signal from the automatic gain control circuit has a bad temperature characteristic (.+-.2 dB or more) based on the external temperature variation (-30.degree. C.-+50.degree. C.). The second conventional temperature compensation method has a disadvantage of increasing consumption power and cost.
On the other hand, a satellite channel monitoring system is disclosed in Japanese Patent Publication No. Heisei 3-101526. The satellite channel monitoring system is adapted to monitor states of satellite channels of self and counterpart stations to readily manage the satellite channels in a satellite communication ground station for communicating with a satellite, more particularly in a satellite communication ground station with no control means for maintaining a satellite output constant. To this end, the satellite channel monitoring system comprises logic means for receiving a self-station transmit signal from the satellite and calculating an attenuation level of a down link from the satellite to the self-station according to the received level. The logic means also receives a transmit signal from the counterpart station and calculates an attenuation level of an up link from the satellite to the counterpart station on the basis of the received level and the calculated attenuation level of the down link from the satellite to the self-station. However, the above-mentioned satellite channel monitoring system does not relate to a technique proposed by the present invention and cannot solve the above conventional problems.